1. Field of the Invention
The subject invention relates to a speed control device of a power winch for drawing construction machinery or transportation machinery, in particular, to a variable speed control device of a power winch.
2. Prior Art
A power winch is a lifting machinery for lifting an object via reeling tight wire rope, and widely used in applications of engineering construction, heavy objects' transportation, and self-aid and buddy aid in case of accidents. To meet the requirement of the operator, it is common to use a dual speed winch to release the wire rope quickly and hook the object, and to operate at a lower speed to ensure the loading security when lifting the object. Some of the prior art dual speed winches are fully mechanical, such as “Dual Speed Winch” of CN2672017Y. The technical solution disclosed by CN2672017Y is that a hand-operated belt brake or an electro-hydraulic shoe brake is used as the primary brake, a hand-operated belt brake is used as the secondary brake, and a bevel gear with curved teeth and an involute cylindrical gear are used as the gear mechanism. Another example is “A Dual Speed Winch Including a Planetary Transmission Mechanism” of CN101062753A, which discloses a technical solution comprising an electrical motor, a gear box, a planetary transmission mechanism, and brakes, etc. The planetary transmission mechanism includes a high-speed planetary transmission mechanism and a low-speed planetary transmission mechanism with different speed ratio. The high-speed planetary pinion carrier of the high-speed planetary transmission mechanism is connected to a high-speed brake, and the low-speed planetary pinion carrier of the low-speed planetary transmission mechanism is connected to a low-speed planetary transmission output shaft, and then to a low-speed brake. Generally, fully mechanical dual speed winches have the properties of, e.g., high load capacity and smooth transmission. However, the former dual speed winch is controlled by the primary brake and the secondary brake, and the latter is controlled by the high-speed brake and the low-speed brake. Accordingly, both of them use two controllers to perform respective control. They have complicated mechanism, which increases the cost of manufacture, and they are difficult to operate, which reduces their security.